A self-compensation method for out-of-plane motion-induced strain error in 2D digital image correlation

Two-dimensional digital image correlation (2D-DIC) is sensitive to out-of-plane motion, which leads to rather poor strain results. Recently, optical extensometers realized by dual-reflector imaging are proposed, which can selfcompensate the strain errors introduced by out-of-plane motion. In this study, we will extend strain measurement from an extensometer to full-field deformation measurement. To this end, first, two corresponding areas of interest (AOIs) are created based on the symmetrical axis of the reference image. Second, the displacement and strain fields of these AOIs are computed with common 2D-DIC algorithm, respectively. Subsequently, high-accuracy deformation results are obtained by taking the average of the deformation of the corresponding calculation points in two AOIs. Two types of uniaxial tensile tests were conducted to validate the feasibility of the proposed self-compensation method. The first experiment indicates that the strain results obtained with the proposed method are in good agreement with those with strain gauges. The results of the second experiment are basically in agreement with those of numerical simulation ANSYS, which demonstrates the feasibility of the proposed method on measurement of nonuniform strain fields. Both the above two experiments demonstrate that the rigid out-of-plane motion will lead to a global strain-field error for common 2D-DIC.